Addition of 0.03% of disodium edetate dihydrate (DED) was determined by observation of colour differences deltaE* in the CIELAB system to give more effective stabilisation of a low level of coloration of Castellani's paint without fuchsine than did 0.02% DED. Increase of the DED addition to 0.04% did not lead to further retardation of the increase in coloration of the preparation.